Diol containing pendant UV absorbing groups are gaining much more importance to stabilize the polyurethane and polyesters against photochemical degradation. Eur. Pat. No. 627452 A1 and 627452 B1 disclose the preparation of diols with pendant UV absorbing moiety and also the preparation of polyurethane and polyesters from diols containing pendant UV absorbing groups. One class of diols disclosed in the above referred European patents is of the general formula 2 below: ##STR3##
This particular class of diols have an amide group present within their molecule, which could be susceptible to hydrolysis. Moreover, the diols disclosed herein bear tertiary amine linkage, which is known for its ability to quench singlet oxygen and make substrate stable towards oxidative degradation.
Eur. Pat. No. 627452 A1 and 627452 B1 also disclose another class of diols of the general formula 3 below: ##STR4##
This particular class of diols were prepared by Manioh reaction with total time duration of 24 h. Whereas the process for the preparation of the diols disclosed herein is much faster having the total preparation time duration of 12 h.
Most thermoplastic polymers and coating compositions are unstable to the extended exposure to ultraviolet light source in atmosphere. Thermoplastics and coatings tend to demonstrate unwanted colour changes and reduced mechanical strength upon exposure to UV radiation. The preliminary effect of ultraviolet radiation on polymers is the formation of free radicals on the polymer chain, which react with atmospheric oxygen. This results in the formation of peroxide groups. Furthermore, decomposition of peroxide groups causes formation of carbonyl groups and chain scission. Irradiation in absence of oxygen causes the increase in crosslinking. Ultimately, this reflects on the mechanical properties and the colour of the polymeric materials. In order to prevent or at least retard the damage caused by these factors, stabilizers are added to the plastics.
UV absorbers are compounds which on addition to the polymers are capable of preventing or retarding the degradation reactions caused by light energy. 2-Hydroxyphenyl benzotriazoles are the one of the most important UV absorbers, which are used commercially. The preparation and use of functional UV absorber in polymers and coatings is well documented in the art.
The utility of monomeric and low molecular weight UV absorbers is limited due to their properties of migration and leaching. This phenomenon could lead to uneven distribution of UV absorbers within the polymeric matrix. Leaching could be even more harmful as the loss of UV absorbers from the polymer matrix could lead to extensive photo-degradation of the substrate. Therefore, in order to prevent the phenomena of migration and leaching, the UV absorbers with polymerizing ability are being developed This particular class of stabilizers would have even distribution within the polymer matrix and also they overcome the phenomena of migration and leaching.